Polycarbonate resins are widely used in optical media fields, electrical, electronic and OA fields, automobile fields, industrial machine fields, medical treatment fields and other industrial fields because of their excellent transparency, heat resistance and impact resistance. However, the aromatic polycarbonates currently in wide use are produced using starting materials obtained from petroleum resources. In light of modern concerns over depletion of petroleum resources and global warming due to carbon dioxide generated by thermal disposal of waste, more environmentally friendly materials with properties similar to aromatic polycarbonates are desired.
In light of these circumstances, anhydrosugar alcohols such as dianhydrohexitols (isomannide, isoidide and isosorbide) can be obtained from the plant-derived starting materials mannitol, iditol and sorbitol, and these are being investigated as renewable resources for production of polymers and especially polyesters and polycarbonates (resources that, unlike depletable natural resources such as petroleum or coal, are themselves renewable: e.g., forest resources, biomass, wind power, small-scale water power and the like). Of these, low-cost starch has been produced as a starting material and used even as a starting material for pharmaceuticals, while polymers employing isosorbide that is commercially available are also being actively investigated (for example, see Patent documents 1-3).
Also being researched are carbonates obtained by copolymerizing glycols, used in polyester starting materials, as diol components together with isosorbide (for example, see Patent documents 4-5). This is because polycarbonates comprising only isosorbide as the diol component are associated with very high melt viscosity due to their rigid structure, rendering them less suitable for molding. Dianhydrohexitols are quite expensive as polymer starting materials, making cost a significant issue. Therefore, copolymerization of inexpensive glycols in a range that allows the necessary polymer properties to be maintained is advantageous in terms of reducing the cost of the starting material.
However, the major problem faced in the prior art is that polymers obtained using anhydrosugar alcohols such as isosorbide have poor color tone compared to ordinary polymers of petroleum crude materials, and this has been an obstacle to their commercialization and further development for use.    [Patent document 1] British Patent No. 1,079,686    [Patent document 2] International Patent Publication No. 1999/054119    [Patent document 3] International Patent Publication No. 2007/013463    [Patent document 4] International Patent Publication No. 2004/111106    [Patent document 5] Japanese Unexamined Patent Publication No. 2003-292603